Treater regeneration

ABSTRACT

Disclosed are embodiments of a method of regenerating a desiccant in an off-line treater of a polyolefin production process. The method may include a heating phase followed by a cooling phase. The heating phase may involve use of a regenerating gas made from heating a treated a recycle stream of the polyolefin production process to regenerate desiccant in an off-line treater. The cooling phase may involve thermosyphoning the regenerating gas, nitrogen, an olefin-free diluent, or combinations thereof in a closed-convection loop of the off-line treater.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

FIELD

This disclosure relates to the regeneration of feed stream treaters inolefin polymerization processes and systems.

BACKGROUND

Polyolefins can be prepared by polymerization of olefins in one or morereactors where feed materials such as diluent, monomer, comonomer andcatalyst are introduced. The catalyst used can be sensitive to processimpurities, or “poisons.” Thus, polyolefin production processesgenerally include treating reactor feeds to remove impurities prior tointroduction of the feeds into the polymerization reactor(s). Techniquesfor treating reactor feeds include using a desiccant which traps theimpurities. Over time, the desiccant can become saturated withimpurities, creating a need for regeneration of the desiccant in orderto maintain effective removal of the impurities. However, currentregeneration processes can be costly, both in terms of nitrogen and fuelgas consumption, and in terms of the costs associated with regenerationtimes being longer than a month in some cases.

SUMMARY

Embodiments of the disclosure include a method of regenerating adesiccant in an off-line treater of a polyolefin production process. Themethod may include a heating phase followed by a cooling phase.

In embodiments, the heating phase may include treating a recycle streamof the polyolefin production process in an on-line treater havingdesiccant to yield a treated recycle stream, heating at least a portionof the treated recycle stream to yield a regenerating gas, regeneratingat least a portion of the desiccant in the off-line treater using theregenerating gas to yield a regenerating effluent stream, separating theregenerating effluent stream into an impurity stream and a regeneratingrecycle stream, and recycling the regenerating recycle stream to theon-line treater.

In embodiments, the cooling phase may include thermosyphoning aregenerating gas, nitrogen, an olefin-free diluent, or combinationsthereof in a closed-convection loop of the off-line treater to cool theoff-line treater to a temperature in the range of from 150° F. (66° C.)to 400° F. (204° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a process flow diagram of an embodiment of apolyolefin production process which utilizing treaters for feed andrecycle streams according to the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Disclosed herein are embodiments which provide for improved regenerationof treaters for feed streams and recycle streams in a polyolefinproduction process. The treaters according to embodiments of thedisclosure include a pair of feed treaters having desiccant (e.g., inone or more desiccant beds) therein for removing water and, in someembodiments, other impurities from a feed stream of the polyolefinproduction process. In operation, at least one of the pair of feedtreaters is on-line (e.g., operates in a continuous mode so as to accepta feed stream and treat the same to yield a treated feed stream) totreat the feed stream of the polyolefin production process which ispassed through the feed treater(s) so as to remove one or moreimpurities. The treated feed stream which flows from the feed treatmentsystem (optionally combined with a treated recycle stream comprising adiluent, with fresh comonomer, or both) passes to a polymerizationreactor where polyolefins (also referred to herein interchangeably withthe term polymer composition) are formed by contacting the olefinmonomer from the treated feed stream with a catalyst system underconditions suitable for the formation of a polymer composition. Aneffluent is recovered from the polymerization reactor and separated torecover the polymer composition in a product stream and the diluent andany unreacted monomer and/or unreacted comonomer in a recycle stream.The recycle stream is treated in other treaters which include one or apair of recycle treaters having desiccant (e.g., one or more desiccantbeds) therein for removing water and, in some embodiments, otherimpurities from the recycle stream. In operation, at least one of thepair of recycle treaters is on-line (e.g., operates in a continuous modeso as to accept the recycle stream and treat same to yield a treatedrecycle stream) to treat the recycle stream of the polyolefin productionprocess which is passed through the recycle treater(s) so as to removeone or more impurities. The treated recycle stream is recycled to thepolymerization reactor.

During the course of operation, the treaters of the polyolefinproduction process may become saturated with impurities, causingimpurities to flow through the treaters and into the polymerizationreactor. An increase in the melt index of the polymer composition and/ora decrease in polymerization efficiency may indicate saturation of thedesiccant in a treater. The feed treaters and recycle treaters areoperated in parallel pairs such that one of the pair of feed treatersand/or one of the pair of recycle treaters may be taken off-line line(e.g., isolated from flow of the feed stream or recycle stream byactuating valves as described hereinbelow) so that the desiccant thereinmay be regenerated while the other of the pair of feed treaters and/orthe other of the pair of the recycle treaters is on-line.

Embodiments of regeneration disclosed herein may additionally oralternatively also utilize thermosyphoning, in a cooling phase ofregeneration, of nitrogen, of the diluent from the treated recyclestream, of an olefin-free diluent, or combinations thereof, as isdescribed in more detail herein.

The disclosed embodiments include the use of at least a portion of thetreated recycle stream to regenerate an off-line treater (e.g., one of apair of feed treaters which is taken off-line for regeneration, one of apair of recycle treaters which is taken off-line for regeneration, orboth). Using at least a portion of the treated recycle stream toregenerate an off-line treater utilizes available recycle diluent in thepolyolefin production process and reduces or negates the need fornitrogen or other regenerating mediums which involve capitalexpenditure, create additional waste, and/or need subsequent separationsand/or storage. Additionally, incorporation of thermosyphoningtechniques disclosed herein reduces the cooling time required for theoff-line treater being regenerated.

Referring to FIG. 1, there is shown a process flow diagram of anembodiment of a polyolefin production process which has a pair of feedtreaters 10 and 15 for a feed stream 100, a polymerization zone 20, aproduct recovery system 30, and a pair of recycle treaters 40 and 45 fora recycle stream 150.

The feed stream 100 may include one or more olefin monomers as well asone or more impurities. The one or more olefin monomers may includelinear or branched olefins having from 2 to 30 carbon atoms. Examples ofolefin monomers include ethylene, propylene, 1-butene, 1-hexene,1-octene, 3-methyl-1-butene, 4-methyl-1-pentene, and combinationsthereof. The one or more impurities may include water, oxygen, carbondioxide, sulfur compounds, alcohols, acetylene, or combinations thereof.Additionally, the feed stream 100 may include one or more othercomponents such as a catalyst, co-catalysts, fresh diluent, additives,or combinations thereof. As discussed herein, the one or more othercomponents may alternatively be added to the polyolefin productionprocess in other locations.

Feed treaters 10 and 15 are operated in parallel such that at least oneof the feed treaters 10 and 15 is on-line to treat (e.g., remove one ormore impurities from) the feed stream 100, while the other of the feedtreaters 10 and 15 is off-line being regenerated, standing by to goon-line, or also on-line but not saturated with impurities. While FIG. 1shows a single pair of feed treaters 10 and 15, it is contemplated thatpolyolefin production processes may include multiple pairs of feedtreaters, for example from 2 to 20 pairs of feed treaters, or from 2 to10 pairs of feed treaters, or from 2 to 5 feed treaters.

Each of the feed treaters 10 and 15 may be a vessel having desiccanttherein arranged in one or more desiccant beds. For example, and withoutlimitation, each treater 10 and 15 may have from 1 to 30, from 1 to 20,or from 1 to 15 desiccant beds. The desiccant is discussed in moredetail herein.

In an embodiment where feed treater 10 is on-line and feed treater 15 isoff-line, valve 103 in stream 102 and valve 105 in stream 104 are in theopen position, and valve 107 in stream 106 and valve 109 in stream 108are in the closed position. Untreated olefin monomer of the feed stream100 flows through valve 103 and stream 102 such that the untreatedolefin monomer is introduced into treater 10. In an embodiment, theuntreated olefin monomer is introduced into the treater 10 at the bottomof said treater 10. The olefin monomer flows through the desiccant bedsin the treater 10, for example, from the bottom to the top of thetreater 10, and one or more impurities are removed from the olefinmonomer by the desiccant contained in the treater 10. The treatedmonomer flows from the treater 10 via stream 104, valve 105, stream 110,and into polymerization zone 20. The flow of the olefin monomer intreater 10 may alternatively be from top to bottom.

In an embodiment where feed treater 15 is on-line and feed treater 10 isoff-line, valve 107 in stream 106 and valve 109 in stream 108 are in theopen position, and valve 103 in stream 102 and valve 105 in stream 104are in the closed position. Untreated olefin monomer of the feed stream100 flows through valve 107 and stream 106 such that the untreatedolefin monomer is introduced into treater 15. In an embodiment, theuntreated olefin monomer is introduced into the treater 15 at the bottomof said treater 15. The olefin monomer flows through the desiccant bedsin the treater 15, for example, from the bottom to the top of thetreater 15, and one or more impurities are removed from the olefinmonomer by the desiccant contained in the treater 15. The treatedmonomer flows from the treater 15 via stream 108, valve 109, stream 110,and into polymerization zone 20. The flow of the olefin monomer intreater 15 may alternatively be from top to bottom.

Treatment conditions include a residence time sufficient to remove atleast a portion of the impurities from the feed stream 100. Treatmentconditions may include a temperature in the range of about 35° F. (about1.6° C.) to about 80° F. (about 27° C.); alternatively, about 40° F.(about 4.4° C.) to about 70° F. (about 21° C.); alternatively, about 45°F. (about 7.2° C.) to about 60° F. (about 15° C.). Treatment conditionsmay include a pressure in the range of about 600 psig (about 4.14 MPa)to about 850 psig (about 5.86 MPa); alternatively, about 700 psig (about4.83 MPa) to about 825 psig (about 5.69 MPa); alternatively, about 750psig (about 5.17 MPa) to about 800 psig (about 5.52 MPa).

The treated feed flowing in stream 104 and/or 108 generally includes alevel of impurities that is less than a level of impurities present inthe feed stream 100. The amount of an impurity or multiple impuritiesmay be measured and monitored in stream 104, stream 108, and feed stream100 using techniques known in the art with the aid of this disclosure,for example, high performance liquid chromatography (HPLC), gaschromatography (GC), or Raman spectroscopy. The impurities may bemeasured in an online apparatus in streams 100, 104 and/or 108, or asample may be taken from any of stream 104, stream 108, and feed stream100 and subsequently analyzed for impurity concentration. Inembodiments, the treated feed flowing in stream 104 and/or 108 mayinclude less than 200 ppm, less than 150 ppm, less than 100 ppm, lessthan 75 ppm, or less than 50 ppm of one or more impurities.

With continued reference to FIG. 1, fresh comonomer (e.g., hexene,butene, or combinations thereof) is illustrated as flowing in stream120, fresh diluent flowing in stream 122, catalyst flowing in stream124, and treated recycle diluent flowing in stream 160 may be combinedwith the treated feed in stream 110 prior to introduction to thepolymerization zone 20. It is contemplated that any combination ofcomonomer, catalyst, fresh diluent, and treated recycle diluent may beadded to the treated feed for introduction into the polymerization zone20 via stream 110; or, any of comonomer, catalyst, fresh diluent, andtreated recycle diluent may be introduced to the polymerization zone 20in other locations of the polyolefin production process, e.g., any ofthe above-cited components may be combined with the components in feedstream 100, or any of the above-cited components may be introduced intothe polymerization zone 20 separately of the feed stream 100 or treatedfeed stream 110. Moreover, while FIG. 1 shows fresh diluent is combinedwith the treated feed in stream 110 before comonomer and treated recyclediluent, which are combined before the catalyst, the order of combiningcomponents which are introduced to the polymerization zone 20 via stream110 may vary according to techniques known to those skilled in the artwith the aid of this disclosure.

The catalyst that can be employed in accordance with the methods andsystems of the present disclosure may comprise any catalyst systemcompatible with and able to produce polyolefins. For example, thecatalyst may be a chromium based catalyst system, a single sitetransition metal catalyst system including both single and multiple (twoor more) metallocene catalyst systems, a Ziegler-Natta catalyst system,or combinations thereof. In embodiments, the catalyst may be activatedfor subsequent polymerization and may or may not be associated with asupport material.

Examples of catalyst systems which can be used are described in U.S.Pat. Nos. 6,355,594; 6,376,415; 6,395,666; 6,511,936; 6,524,987;6,528,448; 6,531,565; 6,534,609; 6,828,268; 6,852,660; 6,911,505;6,911,506; 6,936,667; 6,977,235; 7,056,977; 7,109,277; 7,119,153;7,148,298; 7,163,906; 7,226,886; 7,247,594; 7,378,537; 7,501,372;7,517,939; 8,012,900; 8,119,553; 8,138,113; 8,207,280; 8,288,487;8,383,754; 8,431,729; 8,501,651; 8,703,886; 8,846,841; 8,912,285;8,932,975; and 8,987,394, each of which is incorporated by referenceherein in its entirety.

The diluent may include hydrocarbons which are alkanes. Examples ofsuitable diluents for use in accordance with the present disclosureinclude but are not limited to propane, n-butane, isobutane, n-pentane,isopentane, neopentane, cyclohexane, n-hexane, and heptane. In one ormore specific embodiments, the diluent is selected from propane,isobutane, hexane, heptane, or combinations thereof.

Hydrogen and other additives may also be introduced into thepolymerization zone 20 (e.g. combined in stream 110, introducedseparately, or combined with another component and introduced togetherwith the other component). Hydrogen may be used to control the molecularweight of the polyolefin formed in the polymerization zone 20. Additivesmay include antistatic materials, chain transfer agents, or otheradditives known in the art of polyolefin production processes.

The polymerization zone 20 may include one or more polymerizationreactors capable of polymerizing olefin monomers to produce polyolefinssuch as homopolymers or copolymers. In one or more embodiments, thepolymerization of olefins may include the homopolymerization of ethyleneor propylene; the copolymerization of ethylene and a higher 1-olefin(e.g., 1-butene, 1-pentene, 1-hexene, 1-octene or 1-decene); thecopolymerization of propylene and a higher 1-olefin (e.g., 1-butene,1-pentene, 1-hexene, 1-octene or 1-decene), or combinations thereof (forpolyolefin production processes having multiple reactors). Additionally,the polyolefins produced may be unimodal, bimodal, or multimodal. Aproduced polyolefin may have a first component and a second component.The first component can be a linear low density polyethylene (LLDPE),and the second component can be a high density polyethylene (HDPE). TheHDPE can be a high molecular weight (HMW) polyolefin or a low molecularweight (LMW) polyolefin. The LLDPE can be a high molecular weight (HMW)polyolefin or a low molecular weight (LMW) polyolefin. In an embodiment,the HDPE can be a HMW polyolefin, and the LLDPE can be a LMW polyolefin.The first component, the second component, or both the first componentand the second component of the polyolefin can have short chainbranching.

The various types of reactors suitable for use in the polymerizationzone 20 include those known in the art which may be referred to asbatch, slurry, gas-phase, solution, high pressure, tubular, or autoclavereactors. Batch-type reactors can include continuous flow stirred-tank(CSTR) reactors. Gas phase reactors may include fluidized bed reactorsor staged horizontal reactors. Slurry reactors may include vertical orhorizontal loop reactors. High pressure reactors may include autoclaveand/or tubular reactors, singly or in combination, and optionally inseries. The reactor types can include batch or continuous processes.Batch processes have no product discharge. Continuous processes canutilize intermittent or continuous product discharge. Processes may alsoinclude partial or full direct recycle of un-reacted monomer, un-reactedco-monomer, and/or diluent.

In embodiments where polymerization zone 20 has multiple reactors, theone or more reactors may include the same or different type of reactors.The operating conditions in one of the reactors may be different thanthe operating conditions in the other reactor(s). Multiple reactorsystems may include any combination of reactors including, but notlimited to, multiple loop reactors, multiple gas reactors, a combinationof loop and gas reactors, multiple high pressure reactors, or acombination of high pressure with loop and/or gas reactors. The multiplereactors may be operated in series or in parallel.

Polyolefin production in multiple reactors may include two separatepolymerization reactors interconnected by a transfer system therebymaking it possible to transfer the polyolefin resulting from the firstpolymerization reactor into the second polymerization reactor.Alternatively, polymerization in multiple reactors may include themanual transfer of polyolefin from one reactor to subsequent reactorsfor continued polymerization.

In embodiments where polymerization zone 20 has at least two reactors,the first reactor can produce a first component of a polyolefin product,and the second reactor can produce a second component of a polyolefinproduct. The first component and the second component can have thecharacteristics described above. That is, the first component producedin the first reactor can be a linear low density polyethylene (LLDPE),and the second component produced in the second reactor can be a highdensity polyethylene (HDPE). The LLDPE can be a high molecular weight(HMW) polyolefin or a low molecular weight (LMW) polyolefin. The HDPEcan be a high molecular weight (HMW) polyolefin or a low molecularweight (LMW) polyolefin. In an embodiment, the LLDPE produced in thefirst reactor can be a LMW polyolefin, and the HDPE produced in thesecond reactor can be a HMW polyolefin, and in some embodiments, thefirst component, the second component, or both the first component andthe second component can have short chain branching.

The polymerization conditions within the polymerization zone 20 includetemperature, pressure, flow rate, mechanical agitation, product takeoff,residence time, and concentrations. Any combination of these conditionsmay be selected to achieve the desired polyolefin properties. Conditionsthat are controlled for polymerization efficiency and to provide desiredproduct properties may include temperature, pressure, and theconcentrations of various reactants. Polymerization temperature canaffect catalyst activity, molecular weight of the polyolefin, andmolecular weight distribution of the polyolefin.

Polymerization temperatures may include any temperature below thede-polymerization temperature according to the Gibbs Free energyequation. For example, the polymerization temperature may be in therange of about 140° F. (about 60° C.) to about 536° F. (about 280° C.),or about 158° F. (about 70° C.) to about 230° F. (about 110° C.),depending upon the type of polymerization reactor.

Polymerization pressures also vary according to the reactor andpolymerization type. The pressure for liquid phase polymerizations in aslurry loop reactor may be less than about 1000 psig (about 6.90 MPa)while the pressure for gas phase polymerization may vary from about 200psig (about 1.38 MPa) to about 500 psig (about 3.45 MPa). High pressurepolymerization in tubular or autoclave reactors may run at pressures offrom about 20,000 psig (about 138 MPa) to about 75,000 psig (about 517MPa). Polymerization reactors can also be operated in a supercriticalregion occurring at generally higher temperatures and pressures.

The concentration of the various components (e.g., treated feed, treatedrecycle diluent, catalyst components, comonomer, hydrogen, additives, orcombinations thereof) in the polymerization zone 20 can be controlled toproduce polyolefins having certain physical and mechanical properties.The proposed end-use product that will be formed by the polyolefin(s)and the method of forming that product can determine the desiredproperties. Mechanical properties of the formed end-use product mayinclude tensile, flexural, impact, creep, stress relaxation, andhardness tests. Physical properties of the polyolefin polymer producedmay include density, molecular weight, molecular weight distribution,melting temperature, glass transition temperature, temperature melt ofcrystallization, density, stereoregularity, crack growth, long chainbranching and rheological measurements, for example.

Examples of polymerization processes suitable for use in thepolymerization zone 20 are described in U.S. Pat. Nos. 3,061,601;3,248,179; 4,212,847; 4,501,885; 5,028,670; 5,534,607; 5,565,175;5,575,979; 6,096,840; 6,239,235; 6,833,415; 7,531,606; 7,598,327; and7,652,108, each of which is incorporated by reference herein in itsentirety.

With continued reference to FIG. 1, reaction effluent flows from thepolymerization zone 20 in stream 130 and into a product recovery system30. The product recovery system 30 may include a continuous take-offvalve, a flashline heater for vaporizing liquid components from thepolyolefin (e.g., diluent, unreacted monomer, and unreacted comonomer),a flash vessel for separating the polyolefin product from unreactedmonomer, unreacted comonomer, diluent, residual catalyst, orcombinations thereof. The polyolefin product may flow from the productrecovery system 30 via stream 140, for example, to an extrusion/load-outsystem. Typically, the polyolefin product is in the form of polymerfluff which is further processed into pellets using anextrusion/load-out system for shipment to customers. The unreactedmonomer, unreacted comonomer, diluent, residual catalyst, orcombinations thereof may flow from the product recovery system viastream 150.

The product recovery system 30 may include (in addition to or in thealternative to the flash vessel) one or more fractionation vessels torecover the diluent for recycle to the polymerization zone. For example,the one or more fractionation vessels may (not shown for purposes ofclarity) remove undesirable heavy components (e.g., C₆ hydrocarbons andheavier) and light components (e.g., hydrogen, oxygen, nitrogen,byproducts resulting from the presence of hydrogen/oxygen/nitrogen) fromthe diluent and unreacted monomer/comonomer. The one or morefractionation vessels may also separate unreacted monomer and/orcomonomer from the diluent to yield an olefin-free diluent stream foruse in the regeneration of the treaters as described hereinbelow.Examples of product recovery systems 30 are described in U.S. Pat. Nos.4,501,885; 5,534,607; 5,575,979; 6,096,840; 6,239,235; 6,833,415;7,531,606; and 7,652,108, each of which is incorporated by referenceherein in its entirety. Diluent which is to be recycled to thepolymerization zone 20 may also flow in stream 150 from the productrecovery system 30 to recycle treater 40 and/or 45.

This disclosure contemplates that other configurations may be utilizedto ultimately recover polyolefin product and recycle diluent than theconfiguration shown in FIG. 1. The present disclosure may be applicablefor any polyolefin production process in which a diluent may berecovered from a polymerization zone and subsequently treated for use inregenerating treaters (e.g., feed treaters and recycle treaters) in thepolyolefin production process.

Recycle treaters 40 and 45 are operated in parallel such that at leastone of the recycle treaters 40 and 45 is on-line to treat (e.g., removeone or more impurities from) the recycle diluent in recycle stream 150,while the other of the recycle treaters 40 and 45 is off-line beingregenerated, standing by to go on-line, or also on-line but notsaturated with impurities. While FIG. 1 shows a single pair of recycletreaters 40 and 45, it is contemplated that polyolefin productionprocesses may include multiple pairs of recycle treaters, for examplefrom 2 to 20 pairs of recycle treaters, or from 2 to 10 pairs of recycletreaters, or from 2 to 5 recycle treaters.

Each of the recycle treaters 40 and 45 may be a vessel having desiccanttherein arranged in one or more desiccant beds. For example, eachtreater 40 and 45 may have from 1 to 30, from 1 to 20, or from 1 to 15desiccant beds. The desiccant is discussed in more detail herein.

In an embodiment where recycle treater 40 is on-line and recycle treater45 is off-line, valve 153 in stream 152 and valve 155 in stream 154 arein the open position, and valve 157 in stream 156 and valve 159 instream 158 are in the closed position. Untreated recycle components(e.g., untreated diluent, unreacted monomer, unreacted comonomer, orcombinations thereof) of the recycle stream 150 flow through valve 153and stream 152 such that the untreated recycle components are introducedinto treater 40. In an embodiment, the untreated recycle components areintroduced into the treater 40 at the bottom of said treater 40. Therecycle components flow through the desiccant beds in the treater 40,for example, from the bottom to the top of the treater 40, and one ormore impurities are removed from the recycle components by the desiccantcontained in the treater 40. Treated recycle components (e.g., treateddiluent, unreacted monomer, unreacted comonomer, or combinationsthereof) may flow from the treater 40 via stream 154, valve 155, stream160, stream 110, and into polymerization zone 20. The flow of therecycle components in treater 40 may alternatively be from top tobottom.

In an embodiment where recycle treater 45 is on-line and recycle treater40 is off-line, valve 157 in stream 156 and valve 159 in stream 158 arein the open position, and valve 153 in stream 152 and valve 155 instream 154 are in the closed position. Untreated recycle components(e.g., untreated diluent, unreacted monomer, unreacted comonomer, orcombinations thereof) of the recycle stream 150 flow through valve 157and stream 156 such that the untreated recycle components are introducedinto treater 45. In an embodiment, the untreated recycle components areintroduced into the treater 45 at the bottom of said treater 45. Therecycle components flow through the desiccant beds in the treater 45,for example, from the bottom to the top of the treater 45, and one ormore impurities are removed from the recycle components by the desiccantcontained in the treater 45. The treated recycle components (e.g.,treated diluent, unreacted monomer, unreacted comonomer, or combinationsthereof) may flow from the treater 45 via stream 158, valve 159, stream160, stream 110, and into polymerization zone 20. The flow of therecycle components in the treater 45 may alternatively be from top tobottom.

Recycle treatment conditions include a residence time sufficient toremove at least a portion of the impurities from the recycle stream 150.Treatment conditions may include a temperature in the range of about 35°F. (about 1.6° C.) to about 80° F. (about 27° C.); alternatively, about40° F. (about 4.4° C.) to about 70° F. (about 21° C.); alternatively,about 45° F. (about 7.2° C.) to about 60° F. (about 15° C.). Treatmentconditions may include a pressure in the range of about 600 psig (about4.14 MPa) to about 850 psig (about 5.86 MPa); alternatively, about 700psig (about 4.83 MPa) to about 825 psig (about 5.69 MPa); alternatively,about 750 psig (about 5.17 MPa) to about 800 psig (about 5.52 MPa).

The treated recycle components flowing in stream 154 and/or 158generally includes a level of impurities that is less than a level ofimpurities present in the recycle stream 150. The amount of an impurityor multiple impurities may be measured and monitored in stream 154,stream 158, and recycle stream 150 using techniques known in the artwith the aid of this disclosure, for example, high performance liquidchromatography (HPLC), gas chromatography (GC), or Raman spectroscopy.The impurities may be measured in an online apparatus in streams 150,154, and/or 158, or a sample may be taken from any of stream 154, stream158, and recycle stream 150 and subsequently analyzed for impurityconcentration. In embodiments, the treated recycle components mayinclude less than 200 ppm, less than 150 ppm, less than 100 ppm, lessthan 75 ppm, or less than 50 ppm of impurities.

The disclosure contemplates that the polyolefin production process shownin FIG. 1 may include equipment such as storage tanks (e.g., for storingmonomer, comonomer, diluent, and catalyst), accumulators, valves, pipes,pumps, heat exchangers, agitators, injection apparatus, flow meters,measurement equipment, control system, or combinations thereof which arenot illustrated in FIG. 1 for purposes of clarity.

The desiccant in the one or more desiccant beds in treaters 10, 15, 40,and 45 may be molecular sieve, activated alumina, silica gel,montmorillonite clay, calcium oxide, calcium sulfate, calcium chloride,activated carbon, metal salts, phosphorus-containing desiccantcompounds, or combinations thereof. The term “molecular sieve” refers toa material having a fixed, open-network structure, usually crystalline,that may be used to separate hydrocarbons from the impurities disclosedherein by selective occlusion of one or more of the impurities. Anexample of a molecular sieve is a zeolite, which has a silicate lattice,often in association with aluminum, boron, gallium, iron, and/ortitanium. An example of a zeolite is a 13× molecular sieve. Inaccordance with one or more embodiments, the molecular sieves have apore size of 10 angstroms (Å) or more. An example of activated aluminais sodium treated alumina.

The desiccant beds absorb one or more of the disclosed impurities suchthat such impurities do not pass out of the treaters 10, 15, 40, and 45and into subsequent polymerization reactors (except in cases where atreater is saturated and impurities pass through the treaters). Once thedesiccant in any of treaters 10, 15, 40, and 45 becomes saturated withone or more impurities, regeneration is required.

Regeneration of the desiccant in treaters 10, 15, 40, and 45 generallyinvolves i) taking the treater 10, 15, 40, or 45 off-line, and ii)regenerating the desiccant. Generally, only one of the pair of feedtreaters 10 and 15 and one of the pair of recycle treaters 40 and 45 istaken off-line at a time. It is contemplated that one of the pair offeed treaters 10 and 15 and one of the pair of recycle treaters 40 and45 may be off-line at the same point in time.

Taking a treater 10, 15, 40, or 45 off-line generally involves closingvalves so as to fluidly isolate the treater which is to be takenoff-line. To take treater 10 off-line, valves 103 and 105 are actuatedto the closed position. To take treater 15 off-line, valves 107 and 109are actuated to the closed position. To take treater 40 off-line, valves153, 155, and 237 are actuated to the closed position. To take treater45 off-line, valves 157, 159, and 239 are actuated to the closedposition. It is contemplated that polyolefin production processes mayhave valves and/or piping in different configurations than that shown inFIG. 1, and the particular procedure for rendering a treater off-linemay be different than those described herein while still involvingfluidly isolating the treater from the rest of the polyolefin productionprocess.

Preparing the off-line treater for regeneration generally involvesdepressurizing the off-line treater, and fluidly connecting the off-linetreater to receive the treated recycle stream and to emit impurities ina flow path that is recycled to the recycle treater 40 and/or 45.

Depressurizing the off-line treater generally involves releasingcontents of the off-line treater until the pressure of the treaterreaches a suitable pressure, e.g., about 150 psig (1.03 MPa) or less.The contents of the off-line treater can be released through a purgestream or one of the streams shown in FIG. 1 for treaters 10, 15, 40,and 45.

To fluidly connect the feed treater 10 which is off-line forregeneration, valves 207 and 211 are actuated to the open position suchthat the off-line feed treater 10 is fluidly connected to the treatedrecycle stream 160 (via streams 200, 202, and 206) and to a flow pathwhich is the regenerating effluent stream (which, in FIG. 1, is the flowpath defined by streams 104, 210, 216, and 230). To fluidly connect thefeed treater 15 which is off-line for regeneration, valves 205 and 213are actuated to the open position such that the off-line feed treater 15is fluidly connected to the treated recycle stream 160 (via streams 200,202, and 204) and to a flow path which is the regenerating effluentstream (which, in FIG. 1, is the flow path defined by streams 108, 212,216, and 230). To fluidly connect the recycle treater 40 which isoff-line for regeneration, valves 261 and 221 are actuated to the openposition such that the off-line recycle treater 40 is fluidly connectedto the treated recycle stream 160 (via streams 200, 202, and 260) and toa flow path which is the regenerating effluent stream (which, in FIG. 1,is the flow path defined by streams 220 and 230). To fluidly connect therecycle treater 45 which is off-line for regeneration, valves 271 and223 are actuated to the open position such that the off-line recycletreater 45 is fluidly connected to the treated recycle stream 160 (viastreams 200, 202, and 270) and to a flow path which is the regeneratingeffluent stream (which, in FIG. 1, is the flow path defined by streams222 and 230).

After the treater 10, 15, 40, or 45 is taken off-line, depressurized,and fluidly connected (to the treated recycle stream 160 and to therespective flow path which is the regenerating effluent stream, asdescribed for each treater 10, 15, 40, and 45 above), the process ofregenerating the desiccant therein may commence. The process ofregenerating the desiccant may be divided into phases: a heating phase,a cooling phase, a holding phase, or combinations thereof.

The heating phase includes treating the recycle stream 150 of thepolyolefin production process in an on-line treater (e.g., one or bothof recycle treaters 40 and 45 which are on-line) to yield the treatedrecycle stream 160, heating at least a portion of the treated recyclestream 160 to yield a regenerating gas, regenerating at least a portionof the desiccant in the off-line treater (feed treater 10 or 15 which isoff-line, and/or recycle treater 40 or 45 which is off-line) using theregenerating gas to yield a regenerating effluent stream (described inmore detail below), separating the regenerating effluent stream into animpurity stream 234 and a regenerating recycle stream 232; and recyclingthe regenerating recycle stream 232 to the on-line treater (one or bothof recycle treaters 40 and 45).

The step of treating the recycle stream 150 is performed as describedabove for recycle treaters 40 or 45. When recycle treater 40 is on-line,treated recycle components flow in stream 154 through valve 155 and intotreated recycle stream 160. When recycle treater 45 is on-line, treatedrecycle components flow in stream 158 through valve 159 and into treatedrecycle stream 160.

In the step of heating, a portion (e.g., 1 wt % to 99 wt %, 10 wt % to90 wt %, or 20 wt % to 80 wt %) of the treated recycle stream 160 flowsinto heater 50 via stream 200 where the treated recycle components areheated to a temperature in the range of 400° F. (204° C.) to 600° F.(316° C.) so as to vaporize said components to yield a regenerating gas.The regenerating gas may be the treated recycle components (e.g.,diluent, unreacted monomer, unreacted comonomer, or combinationsthereof) in gaseous phase. In embodiments, the regenerating gas mayadditionally include nitrogen; alternatively, the regenerating gas maynot include (exclude) nitrogen. The regenerating gas may flow from theheater 50 in stream 202. The heater 50 may be any heating system knownin the art such as a heat exchanger, an electric heater, or acombination thereof connected in series. Examples of a heating system ofheater 50 are found in U.S. Pat. Nos. 2,625,915 and 3,585,971, each ofwhich is incorporated herein by reference in its entirety.

The step of regenerating may include introducing the regenerating gasinto the off-line treater being regenerated, and removing an impurity(e.g., of the one or more impurities discussed herein) from thedesiccant in the off-line treater with the regenerating gas. In the stepof regenerating, the regenerating gas may flow via stream 202 to one ofthe pair of feed treaters 10 and 15 which is off-line for regeneration,to one of the pair of recycle treaters 40 and 45 which is off-line forregeneration, or both. When feed treater 10 is off-line forregeneration, the regenerating gas flows via stream 202, valve 207, andstream 206 for introduction to the feed treater 10. When feed treater 15is off-line for regeneration, the regenerating gas flows via stream 202,valve 205, and stream 204 for introduction to the feed treater 15. Whenrecycle treater 40 is off-line for regeneration, the regenerating gasflows via stream 202, valve 261, and stream 260 for introduction to therecycle treater 40. When recycle treater 45 is off-line forregeneration, the regenerating gas flows via stream 202, valve 271, andstream 270 for introduction to the recycle treater 45. In embodiments,the regenerating gas passes through the desiccant in the off-linetreater being regenerated from bottom to top. Alternatively, theregeneration gas may flow through the off-line treater from top tobottom.

The regenerating gas passes through the desiccant (e.g., in one or moredesiccant beds) of the off-line treater being regenerated during theheating phase as the temperature increases to the temperature ofregeneration, e.g. a temperature in the range of about 400° F. (204° C.)to 600° F. (about 316° C.), or about 450° F. (about 232° C.) to about600° F. (about 316° C.). The pressure of the off-line treater mayincrease as the temperature increases, and the regeneration pressureincludes a pressure in the range of about 600 psig (about 4.14 MPa) toabout 850 psig (about 5.86 MPa), about 700 psig (about 4.83 MPa) toabout 825 psig (about 5.69 MPa), or about 750 psig (about 5.17 MPa) toabout 800 psig (about 5.52 MPa). Alternatively, the pressure of theoff-line treater may be maintained at a regeneration pressure during theheating phase, e.g., for feed treater 10, using stream 14 (e.g., apressure supply steam) having appropriate valve 13 for maintaining thepressure of the feed treater 10. Likewise, stream 18 (e.g., a pressuresupply stream) having appropriate valve 19 may be used for maintainingthe pressure of the feed treater 15 during the heating phase, stream 44(e.g., a pressure supply steam) having appropriate valve 43 may be usedfor maintaining the pressure of the recycle treater 40 during theheating phase, and stream 48 (e.g., a pressure supply steam) havingappropriate valve 49 may be used for maintaining the pressure of therecycle treater 45 during the heating phase. For maintaining thepressure of the off-line treater being regenerated, pressurized nitrogengas may be used.

The regenerating gas together with one or more impurities of thedesiccant flows from the off-line treater being regenerated in aregenerating effluent stream to a separator 60. For feed treater 10, theregenerating effluent stream is defined by streams 104, 210, 216, and230. For feed treater 15, the regenerating effluent stream is defined bystreams 108, 212, 216, and 230. For recycle treater 40, the regeneratingeffluent stream is defined by streams 220 and 230. For recycle treater45, the regenerating effluent stream (as illustrated in FIG. 1) is theflow path defined by streams 222 and 230.

In the step of separating the regenerating effluent stream, theseparator 60 separates the components of the regenerating effluentstream into an impurity stream 234 and a regenerating recycle stream232. The separator 60 may be a condenser which is configured to cool thecomponents of the regenerating effluent stream such that at least one ofthe components condenses and separates so as to yield the impuritystream and the regenerating recycle stream.

For example, in embodiments where the one or more impurities in theregenerating effluent stream include water, the gaseous diluent(optionally also with unreacted monomer, unreacted comonomer, or both)and water vapor may condense in separator 60 to for the liquid phase ofwater and the liquid phase of diluent (optionally also with unreactedmonomer, unreacted comonomer, or both). The liquid phase of water andthe liquid phase of diluent may phase separate from one another. It iscontemplated that other impurities may dissolve and separate from thediluent with the water. It is also contemplated that any unreactedmonomer and any unreacted comonomer may dissolve in the diluent liquidphase and separate from water with the liquid diluent. In an embodiment,the separator 60 and heater 50 may include the same device which is across exchanger which allows the hot gaseous components of theregenerating effluent stream to heat the treated recycle componentsflowing from the treated recycle stream 160 (and for the treated recyclecomponents to cool the gaseous components of the regenerating effluentstream). The one or more phase-separated impurities may flow from theseparator 60 via stream 234 into a knockout pot 80, where impurities maybe flared via stream 240 or may flow from the knockout pot 80 via stream241 for waste disposal (e.g., wastewater disposal). Appropriateequipment may be included in the regenerating recycle stream such thatthe temperature and pressure of the liquid phase diluent flowing thereinis appropriate for flow to the recycle treater 40 and/or 45.

In other embodiments, the separator 60 may separate the one or moreimpurities which are lighter than the gaseous diluent by condensing thediluent to a liquid phase while the one or more impurities remain in thegaseous phase. In yet other embodiments, the separator 60 may separatethe one or more impurities (e.g., water) which are heavier than thegaseous diluent by condensing the water vapor to the liquid phase ofwater while the diluent (optionally, also any unreacted monomer and anyunreacted comonomer) remains in the gaseous phase. In such embodiments,the gaseous phase diluent may be condensed, compressed, or both to aliquid phase for recycle to the recycle treaters 40 and/or 45, or thegaseous phase diluent may flow to the recycle treater 40 and/or 45without further equipment processing.

In the step of recycling, the gaseous phase of diluent (optionally alsounreacted monomer, unreacted comonomer, or both) recovered from theseparator 60 is recycled back to one or both of recycle treaters 40 and45 which are on-line. For example, the flow path which is stream 232,valve 237, stream 236, and stream 152 defines the regenerating recyclestream which recycles the components recovered from the separator 60 tothe recycle treater 40. The flow path which is stream 232, valve 239,stream 238, and stream 156 defines the regenerating recycle stream whichrecycles the components recovered from the separator 60 to the recycletreater 45. Recycling the components used to regenerate an off-linetreater to one or both of recycle treaters 40 and 45 which are on-lineaccounts for any residual impurities that remain in the liquid diluentafter separation in separator 60. In such embodiments, the recycletreater 40 and/or 45 may remove residual impurities from the componentsof the regenerating recycle stream which are introduced to said recycletreater 40 and/or 45.

In embodiments, the heating phase may be performed in the absence ofnitrogen.

Once the temperature of regeneration is reached in the off-line treaterbeing regenerated, the method of regenerating the desiccant in theoff-line treater may enter a holding phase followed by a cooling phase,the method may enter directly to the cooling phase without a holdingphase, or the method may enter into the cooling phase followed by aholding phase.

In the holding phase before the cooling phase, the temperature of theoff-line treater being regenerated may be maintained at the regenerationtemperature for a period of time. For example, the temperature may bemaintained for about 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or morehours. During the holding phase, the regenerating gas may continue topass though the desiccant and out of the off-line treater, or flow ofthe regenerating gas through the off-line treater may be stopped. Inembodiments of the holding phase which continue the flow of regeneratinggas through the off-line treater, heating of the treated recyclecomponents in heater 50 may continue in order to maintain thetemperature of the off-line treater at the regenerating temperature.

In a cooling phase which is performed directly after the heating phaseor after the holding phase, the method for regenerating the off-linetreater includes thermosyphoning the regenerating gas, nitrogen, anolefin-free diluent, or combinations thereof in a closed-convection loopof the off-line treater to cool the off-line treater to a temperature inthe range of about 150° F. (66° C.) to about 400° F. (204° C.).

To begin the cooling phase of regenerating the off-line treater, theflow of regenerating gas is stopped, said off-line treater isblocked-in, and the closed-convection loop is opened. To stop the flowof regenerating gas to the feed treater 10 which is off-line, valve 207is actuated to the closed position. To block-in the feed treater 10,valve 211 is also actuated to the closed position, making all valves instreams entering and exiting the feed treater 10 set to the closedposition (valves 103 and 105 having previously been closed). To open theclosed-convection loop 12 of the feed treater 10, valve 27 is actuatedto the open position. The flow of regenerating gas to feed treater 15 issimilarly stopped by actuating valve 205 to the closed position, saidfeed treater 15 is similarly blocked-in by actuating valve 213 to theclosed position, and the closed-convection loop 16 of the feed treater15 is opened by actuating value 21 to the open position. Likewise, theflow of regenerating gas to recycle treater 40 is stopped by actuatingvalve 261 to the closed position, said recycle treater 15 is blocked-inby actuating valve 221 to the closed position, and the closed-convectionloop 42 of the recycle treater 40 is opened by actuating valve 23 to theopen position. Finally, the flow of regenerating gas to recycle treater45 is similarly stopped by actuating valve 159 to the closed position,said recycle treater 45 is similarly blocked-in by actuating value 223to the closed position, and the closed-convection loop 46 of the recycletreater 45 is opened by actuating valve 25 to the open position.

Each closed-convection loop 12, 16, 42, and 46 of treater 10, 15, 40,and 45 includes a cooler 11, 17, 41, and 47, respectively. In theembodiment illustrated in FIG. 1, the coolers 11, 17, 41, and 47 arefinned air coolers, although any acceptable cooler may be used inaccordance with the present disclosure. Generally, eachclosed-convection loop 12, 16, 42, and 46 has an end connected to thetop and an end connected to the bottom of the treater 10, 15, 40, and45, respectively. Each cooler 11, 17, 41, 47 is positioned in theclosed-convection loop 12, 16, 42, 46 proximate the end which isconnected to the top of the treater 10, 15, 40, 45.

For feed treaters 10 and 15, nitrogen or the regenerating gas can beused in thermosyphoning whichever one of the feed treaters 10 or 15 isoff-line. For purposes of efficiency, the feed treater 10 is discussedwith the intention that the same thermosyphoning technique applies tofeed treater 15.

In embodiments which use nitrogen for thermosyphoning the feed treater10, nitrogen is added to the feed treater 10 via stream 14 (e.g., anitrogen supply stream) and valve 13. In embodiments which use nitrogen,the regenerating gas can be previously removed from the feed treater 10before blocking-in the feed treater 10. The nitrogen is drawn out of thetop of the feed treater 10 into the closed-convection loop 12. Thenitrogen experiences convective cooling in the cooler 11, and naturalconvection causes the cooled nitrogen to flow further into theclosed-convection loop 12 until the cooled nitrogen flows back into thebottom of the feed treater 10. The cooled nitrogen which enters thebottom of the feed treater 10 from the closed-convection loop 12 isheated by the cooling desiccant, which causes the nitrogen to warm andrise to the top of the feed treater 10, where flow through theclosed-convection loop 12 is repeated. Circulation of nitrogen throughthe closed-convection loop 12 occurs due to temperature gradients in theoff-line treater 10. Circulation may be stopped when the temperature ofthe feed treater 10 (e.g., measured in the desiccant therein or as thenitrogen temperature at a point in the treater 10 or in theclosed-convection loop 12) reaches a cooled temperature in the range of150° F. (66° C.) to 400° F. (204° C.). The pressure of the feed treater10 (which is off-line) can be maintained during thermosyphoning withnitrogen through nitrogen pressure supplied via stream 14 (e.g., anitrogen pressure supply stream).

In embodiments which use the regenerating gas for thermosyphoning thefeed treater 10, the regenerating gas remaining in the feed treater 10after stopping the regenerating gas flow and blocking-in of the feedtreater 10 is drawn out of the top of the feed treater 10 into theclosed-convection loop 12. The regenerating gas experiences convectivecooling in the cooler 11, and natural convection causes the cooledregenerating gas to flow further into the closed-convection loop 12until the cooled regenerating gas flows back into the bottom of the feedtreater 10. The cooled regenerating gas which enters the bottom of thefeed treater 10 from the closed-convection loop 12 is heated by thecooling desiccant, which causes the regenerating gas to warm and rise tothe top of the feed treater 10, where flow through the closed-convectionloop 12 is repeated. Circulation of the regenerating gas through theclosed-convection loop 12 occurs due to temperature gradients in theoff-line treater 10. Circulation may be stopped when the temperature ofthe feed treater 10 (e.g., measured in the desiccant therein or as theregenerating gas temperature at a point in the treater 10 or in theclosed-convection loop 12) reaches a cooled temperature in the range of150° F. (66° C.) to 400° F. (204° C.). In an embodiment, use of theregenerating gas for thermosyphoning the feed treater 10 may be in theabsence of nitrogen.

For recycle treaters 40 and 45, nitrogen, the regenerating gas, olefinfree diluent, or combinations thereof can be used in thermosyphoningwhichever one of the recycle treaters 40 or 45 is off-line. For purposesof efficiency, the recycle treater 40 is discussed with the intentionthat the same thermosyphoning technique applies to recycle treater 45.

In embodiments which use nitrogen for thermosyphoning the recycletreater 40, nitrogen is added to the recycle treater 40 via stream 44(e.g., a nitrogen supply stream) and valve 43. In embodiments which usenitrogen, the regenerating gas can be previously removed from therecycle treater 40 before blocking-in the recycle treater 40. Thenitrogen is drawn out of the top of the recycle treater 40 into theclosed-convection loop 42. The nitrogen experiences convective coolingin the cooler 41, and natural convection causes the cooled nitrogen toflow further into the closed-convection loop 42 until the coolednitrogen flows back into the bottom of the recycle treater 40. Thecooled nitrogen which enters the bottom of the recycle treater 40 fromthe closed-convection loop 42 is heated by the cooling desiccant, whichcauses the nitrogen to warm and rise to the top of the recycle treater40, where flow through the closed-convection loop 42 is repeated.Circulation of nitrogen through the closed-convection loop 42 occurs dueto temperature gradients in the off-line treater 40. Circulation may bestopped when the temperature of the recycle treater 40 (e.g., measuredin the desiccant therein or as the nitrogen temperature at a point inthe treater 40 or in the closed-convection loop 42) reaches a cooledtemperature in the range of 150° F. (66° C.) to 400° F. (204° C.). Thepressure of the recycle treater 40 (which is off-line) can be maintainedduring thermosyphoning with nitrogen through nitrogen pressure suppliedvia stream 44 (e.g., a nitrogen pressure supply stream).

In embodiments which use the regenerating gas for thermosyphoning therecycle treater 40, the regenerating gas remaining in the recycletreater 40 after stopping the regenerating gas flow and blocking-in ofthe recycle treater 40 is drawn out of the top of the recycle treater 40into the closed-convection loop 42. The regenerating gas experiencesconvective cooling in the cooler 41, and natural convection causes thecooled regenerating gas to flow further into the closed-convection loop42 until the cooled regenerating gas flows back into the bottom of therecycle treater 40. The cooled regenerating gas which enters the bottomof the recycle treater 40 from the closed-convection loop 42 is heatedby the cooling desiccant, which causes the regenerating gas to warm andrise to the top of the recycle treater 40, where flow through theclosed-convection loop 42 is repeated. Circulation of regenerating gasthrough the closed-convection loop 42 occurs due to temperaturegradients in the off-line treater 40. Circulation may be stopped whenthe temperature of the recycle treater 40 (e.g., measured in thedesiccant therein or as the regenerating gas temperature at a point intreater 40 of in the closed-convection loop 42) reaches a cooledtemperature in the range of 150° F. (66° C.) to 400° F. (204° C.). In anembodiment, use of the regenerating gas for thermosyphoning the recycletreater 40 may be in the absence of nitrogen.

In embodiments which use a combination of nitrogen, the regeneratinggas, and olefin-free diluent for thermosyphoning, two stages areperformed. First, nitrogen, the regenerating gas, or both isthermosyphoned in the closed-convection loop 42 of the recycle treater40 as described above to cool the recycle treater 40 to a firsttemperature of about 350° F. (about 177° C.). Second, an olefin-freediluent (e.g., obtained from product recovery system 30) is introducedinto the recycle treater 40 and then thermosyphoned in theclosed-convection loop 42 of the recycle treater 40 in a manner similarto that described above for the regenerating gas and nitrogen to coolthe recycle treater 40 from the first temperature to the a secondtemperature of about 150° F. (about 66° C.). In an embodiment of thesecond stage, the regenerating gas and/or the nitrogen used inthermosyphoning is removed such that the olefin-free diluent is thepredominant (e.g., greater than 95, 96, 97, 98, 99, or more vol % of thetreater 40) regenerating material in the recycle treater 40 in thesecond stage of the cooling phase.

In the holding phase after the cooling phase, the temperature of theoff-line treater being regenerated may be maintained at the cooledtemperature for a period of time. For example, the temperature may bemaintained for less than 1 hour, or for about 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more hours.

Utilization of thermosyphoning in combination with a cooler in theclosed-convection loop reduces the cooling time for the cooling phase.

Regeneration of treaters 10, 15, 40, and 45 reduces the amount of theone or more impurities in the treaters 10, 15, 40, and 45. Embodimentscontemplate the amount of impurities may be measured and monitored instream 104 for feed treater 10, in stream 108 for feed treater 15, instream 154 for recycle treater 40, and in stream 158 for recycle treater45. Monitoring and measuring of the impurities enables regeneration fora time sufficient to reduce the impurities in the regenerating effluentstream passing stream 104, 108, 154, or 158 to a desired level (e.g.,less than 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3,2, 1, or less ppm based on weight of the regenerating effluent stream).Impurity levels may be measured using techniques known in the art withthe aid of this disclosure, for example, high performance liquidchromatography (HPLC), gas chromatography (GC), or Raman spectroscopy.The impurities may be measured in an online apparatus in streams 104,108, 150, and/or 154, or a sample may be taken from any of streams 104,108, 154, and/or 158 and subsequently analyzed for impurityconcentration.

After regeneration, the off-line treater remains in stand-by mode untilthe other of the pair of treaters needs regeneration. Alternatively,after regeneration, the off-line treater is brought on-line without anystand-by. To take treater 10 on-line, valves 103 and 105 are actuated tothe open position. To take treater 15 on-line, valves 107 and 109 areactuated to the open position. To take treater 40 on-line, valves 153,155, and 237 are actuated to the open position. To take treater 45on-line, valves 157, 159, and 239 are actuated to the open position.

Utilizing at least a portion of the treated recycle stream as theregenerating gas in at least part of the regeneration process (e.g., inthe heating phase, a holding phase, the cooling phase, or combinationsthereof) of a treater reduces the amount of nitrogen needed forregeneration and utilizes an already existing supply of regeneratingmaterial (e.g., the treated recycle components) for regeneratingtreaters. Using less nitrogen reduces the nitrogen supply burden neededfor modern polyolefin production processes, which saves costs and freesnitrogen supply for other uses in the polyolefin production process.Moreover, using less nitrogen results in fewer NO_(x) emissions at theflare since the treated recycle components (which are recycled to therecycle treaters 40 and 45 and not flared) can be used in place ofnitrogen for regeneration. Further utilizing the existing supply oftreated recycle components for regeneration eliminates any cost forobtaining regenerating materials.

ADDITIONAL DESCRIPTION

Embodiments of methods for treater regeneration have been described. Thefollowing are a first set of nonlimiting, specific embodiments inaccordance with the present disclosure:

Embodiment 1 is a method of regenerating a desiccant in an off-linetreater of a polyolefin production process, the method comprising aheating phase followed by a cooling phase, the heating phase comprisingtreating a recycle stream of the polyolefin production process in anon-line treater to yield a treated recycle stream; heating at least aportion of the treated recycle stream to yield a regenerating gas;regenerating at least a portion of the desiccant in the off-line treaterusing the regenerating gas to yield a regenerating effluent stream;separating the regenerating effluent stream into an impurity stream anda regenerating recycle stream; and recycling the regenerating recyclestream to the on-line treater.

Embodiment 2 is the method of embodiment 1, the cooling phase comprisingthermosyphoning the regenerating gas, nitrogen, or both in aclosed-convection loop of the off-line treater to cool the off-linetreater to a temperature in the range of 150° F. (66° C.) to 400° F.(204° C.).

Embodiment 3 is the method of embodiment 2, wherein theclosed-convection loop comprises a finned air cooler.

Embodiment 4 is the method of embodiment 1, the cooling phase comprisingthermosyphoning the regenerating gas, nitrogen, or both in aclosed-convection loop of the off-line treater to cool the off-linetreater to a first temperature of about 350° F. (about 177° C.); andthermosyphoning an olefin-free diluent in the closed-convection loop ofthe off-line treater to cool the off-line treater from the firsttemperature to a second temperature of about 150° F. (about 66° C.).

Embodiment 5 is the method of embodiment 4, wherein theclosed-convection loop comprises a finned air cooler.

Embodiment 6 is the method of any of embodiments 1 to 5, wherein theoff-line treater reaches a temperature in the range of 400° F. to (204°C.) to 600° F. (316° C.) during the heating phase.

Embodiment 7 is the method of any of embodiments 1 to 6, wherein thestep of regenerating comprises introducing the regenerating gas into theoff-line treater; and removing an impurity from the desiccant of theoff-line treater with the regenerating gas.

Embodiment 8 is the method of any of embodiments 1 to 7, wherein thestep of separating comprises condensing the regenerating effluent streamto yield the impurity stream and the regenerating recycle stream.

Embodiment 9 is the method of any of embodiments 1 to 8, wherein therecycle stream of the polyolefin production process, the treated recyclestream, the regenerating gas, the regenerating effluent stream, and theregenerating recycle stream each comprise one or more compounds selectedfrom the group consisting of diluent, unreacted monomer, unreactedcomonomer, and combinations thereof.

Embodiment 10 is the method of any of embodiments 1 to 9, wherein theregenerating gas and the regenerating effluent stream comprise diluentin a gaseous phase.

Embodiment 11 is the method of any of embodiments 1 to 10, wherein therecycle stream, the treated recycle stream, and the regenerating recyclestream comprise diluent in a liquid phase.

Embodiment 12 is the method of any of embodiments 1 to 11, wherein thediluent is propane, butane, isobutane, pentane, isopentane, hexane,heptane, or combinations thereof.

Embodiment 13 is the method of any of embodiments 1 to 12, wherein theunreacted monomer is ethylene, propylene, octene (e.g., 1-octene), orcombinations thereof.

Embodiment 14 is the method of any of embodiments 1 to 13, wherein theunreacted comonomer is hexene, butene, or combinations thereof.

Embodiment 15 is the method of any of embodiments 1 to 14, wherein thedesiccant is arranged in one or more desiccant beds in the off-linetreater.

Embodiment 16 is the method of embodiment 15, wherein the one or moredesiccant beds are selected from molecular sieve, activated alumina,silica gel, montmorillonite clay, calcium oxide, calcium sulfate,calcium chloride, activated carbon, metal salts, phosphorus-containingdesiccant compounds, or combinations thereof.

Embodiment 17 is the method of embodiment 16, wherein the one or moredesiccant beds comprise a molecular sieve having a pore size of 10angstroms or more.

Embodiment 18 is the method of any of embodiments 1 to 17, wherein thepolyolefin production process comprises from 2 to 40 treaters.

Embodiment 19 is the method of embodiment 18, wherein each treatercomprises from 1 to 30 desiccant beds.

Embodiment 20 is the method of any of embodiments 18 to 19, wherein eachtreater is a feed treater or a recycle treater.

Embodiment 21 is a method of regenerating a desiccant in an off-linetreater of a polyolefin production process, the method comprising aheating phase followed by a cooling phase, the cooling phase comprisingthermosyphoning a regenerating gas, nitrogen, an olefin-free diluent, orcombinations thereof in a closed-convection loop of the off-line treaterto cool the off-line treater to a temperature in the range of from 150°F. (66° C.) to 400° F. (204° C.).

Embodiment 22 is the method of embodiment 21, wherein the step ofthermosyphoning comprises thermosyphoning the regenerating gas,nitrogen, or both in the closed-convection loop of the off-line treaterto cool the off-line treater to a first temperature of about 350° F.(about 177° C.); and thermosyphoning the olefin-free diluent in theclosed-convection loop of the off-line treater to cool the off-linetreater from the first temperature to a second temperature of about 150°F. (about 66° C.).

Embodiment 23 is the method of any of embodiments 21 to 22, wherein theclosed-convection loop comprises a finned air cooler.

Embodiment 24 is the method of any of embodiments 21 to 23, wherein theregenerating gas is obtained by treating a recycle stream of thepolyolefin production process in an on-line treater to yield a treatedrecycle stream; heating at least a portion of the treated recycle streamto yield the regenerating gas; and introducing the regenerating gas tothe off-line heater.

Embodiment 25 is the method of any of embodiments 21 to 24, furthercomprising maintaining a pressure of the off-line treater during thestep of thermosyphoning.

Embodiment 26 is the method of any of embodiments 21 to 25, wherein theoff-line treater reaches a temperature in the range of 400° F. (204° C.)to 600° F. (316° C.) during the heating phase.

Embodiment 27 is the method of any of embodiments 21 to 26, furthercomprising a holding phase between the heating phase and the coolingphase, wherein holding phase comprises maintaining the off-line treaterat the temperature in the range of 400° F. (204° C.) to 600° F. (316°C.).

Embodiment 28 is the method of any of embodiments 21 to 27, wherein arecycle stream of the polyolefin production process, the treated recyclestream, the regenerating gas, a regenerating effluent stream, and aregenerating recycle stream each comprise one or more compounds selectedfrom the group consisting of diluent, unreacted monomer, unreactedcomonomer, and combinations thereof.

Embodiment 29 is the method of embodiment 28, wherein the regeneratinggas and the regenerating effluent stream comprise diluent in a gaseousphase.

Embodiment 30 is the method of any of embodiments 28 to 29, wherein therecycle stream, the treated recycle stream, and the regenerating recyclestream comprise diluent in a liquid phase.

Embodiment 31 is the method of any of embodiments 21 to 30, wherein thediluent is propane, butane, isobutane, pentane, isopentane, hexane,heptane, or combinations thereof.

Embodiment 32 is the method of any of embodiments 28 to 31, wherein theunreacted monomer is ethylene, propylene, octene (e.g., 1-octene), orcombinations thereof.

Embodiment 33 is the method of any of embodiments 28 to 32, wherein theunreacted comonomer is hexene, butene, or combinations thereof.

Embodiment 34 is the method of any of embodiments 21 to 33, wherein thedesiccant is arranged in one or more desiccant beds in the off-linetreater.

Embodiment 35 is the method of embodiment 34, wherein the one or moredesiccant beds are selected from molecular sieve, activated alumina,silica gel, montmorillonite clay, calcium oxide, calcium sulfate,calcium chloride, activated carbon, metal salts, phosphorus-containingdesiccant compounds, or combinations thereof.

Embodiment 36 is the method of embodiment 35, wherein the one or moredesiccant beds comprise a molecular sieve having a pore size of 10angstroms or more.

Embodiment 37 is the method of any of embodiments 21 to 36, wherein thepolyolefin production process comprises from 2 to 40 treaters.

Embodiment 38 is the method of embodiment 37, wherein each treatercomprises from 1 to 30 desiccant beds.

Embodiment 39 is the method of any of embodiments 37 to 38, wherein eachtreater is a feed treater or a recycle treater.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). Use of theterm “optionally” with respect to any element of a claim is intended tomean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The discussion of a reference in the disclosure is not an admission thatit is prior art to the present invention, especially any reference thatmay have a publication date after the priority date of this application.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference, to the extent thatthey provide exemplary, procedural or other details supplementary tothose set forth herein.

What is claimed is:
 1. A method of regenerating a desiccant in anoff-line treater of a polyolefin production process, the methodcomprising a heating phase followed by a cooling phase, the heatingphase comprising: treating a recycle stream of the polyolefin productionprocess in an on-line treater to yield a treated recycle stream; heatingat least a portion of the treated recycle stream to yield a regeneratinggas; regenerating at least a portion of the desiccant in the off-linetreater using the regenerating gas to yield a regenerating effluentstream; separating the regenerating effluent stream into an impuritystream and a regenerating recycle stream; and recycling the regeneratingrecycle stream to the on-line treater.
 2. The method of claim 1, thecooling phase comprising: thermosyphoning the regenerating gas,nitrogen, or both in a closed-convection loop of the off-line treater tocool the off-line treater to a temperature in the range of 150° F. (66°C.) to 400° F. (204° C.).
 3. The method of claim 2, wherein theclosed-convection loop comprises a finned air cooler.
 4. The method ofclaim 1, the cooling phase comprising: thermosyphoning the regeneratinggas, nitrogen, or both in a closed-convection loop of the off-linetreater to cool the off-line treater to a first temperature of about350° F. (about 177° C.); and thermosyphoning an olefin-free diluent inthe closed-convection loop of the off-line treater to cool the off-linetreater from the first temperature to a second temperature of about 150°F. (about 66° C.).
 5. The method of claim 1, wherein the off-linetreater reaches a temperature in the range of 400° F. (204° C.) to 600°F. (316° C.) during the heating phase.
 6. The method of claim 1, whereinthe step of regenerating comprises: introducing the regenerating gasinto the off-line treater; and removing an impurity from the desiccantof the off-line treater with the regenerating gas.
 7. The method ofclaim 1, wherein the step of separating comprises: condensing theregenerating effluent stream to yield the impurity stream and theregenerating recycle stream.
 8. The method of claim 1, wherein therecycle stream of the polyolefin production process, the treated recyclestream, the regenerating gas, the regenerating effluent stream, and theregenerating recycle stream each comprise one or more compounds selectedfrom the group consisting of diluent, unreacted monomer, unreactedcomonomer, and combinations thereof.
 9. The method of claim 8, whereinthe regenerating gas and the regenerating effluent stream comprisediluent in a gaseous phase.
 10. The method of claim 8, wherein therecycle stream, the treated recycle stream, and the regenerating recyclestream comprise diluent in a liquid phase.
 11. The method of claim 8,wherein the diluent is propane, butane, isobutane, pentane, isopentane,hexane, heptane, or combinations thereof.
 12. The method of claim 8,wherein the unreacted monomer is ethylene, propylene, octene, orcombinations thereof.
 13. The method of claim 8, wherein the unreactedcomonomer is hexene, butene, or combinations thereof.
 14. A method ofregenerating a desiccant in an off-line treater of a polyolefinproduction process, the method comprising a heating phase followed by acooling phase, the cooling phase comprising: thermosyphoning aregenerating gas, nitrogen, an olefin-free diluent, or combinationsthereof in a closed-convection loop of the off-line treater to cool theoff-line treater to a temperature in the range of from 150° F. (66° C.)to 400° F. (204° C.).
 15. The method of claim 14, wherein the step ofthermosyphoning comprises: thermosyphoning the regenerating gas,nitrogen, or both in the closed-convection loop of the off-line treaterto cool the off-line treater to a first temperature of about 350° F.(about 177° C.); and thermosyphoning the olefin-free diluent in theclosed-convection loop of the off-line treater to cool the off-linetreater from the first temperature to a second temperature of about 150°F. (about 66° C.).
 16. The method of claim 14, wherein theclosed-convection loop comprises a finned air cooler.
 17. The method ofclaim 14, wherein the regenerating gas is obtained by: treating arecycle stream of the polyolefin production process in an on-linetreater to yield a treated recycle stream; heating at least a portion ofthe treated recycle stream to yield the regenerating gas; andintroducing the regenerating gas to the off-line heater.
 18. The methodof claim 14, further comprising: maintaining a pressure of the off-linetreater during the step of thermosyphoning.
 19. The method of claim 14,wherein the off-line treater reaches a temperature in the range of 400°F. (204° C.) to 600° F. (316° C.) during the heating phase.
 20. Themethod of claim 19, further comprising a holding phase between theheating phase and the cooling phase, wherein holding phase comprises:maintaining the off-line treater at the temperature in the range of 400°F. (204° C.) to 600° F. (316° C.).